A wide variety of heat exchange apparatus has been used for treatment of exit gases from process streams, particularly those containing corrosive elements such as combustion gases. Such combustion gases typically contain oxides of sulfur and nitrogen that can form highly corrosive acids. These acids have restricted the materials that can be used in heat exchange apparatus when the gas is cooled below its dew point. To compensate for the highly corrosive nature of such gases, heat exchange elements have, in the past, been prepared from glass, copper, and copper covered with fluoropolymer. Moreover, highly structured arrangements of fluoropolymer tubes have been suggested, such as in Withers U.S. Pat. No. 3,435,893.
When recovering heat from exit gases resulting from combustion processes, a continuing difficulty is encountered in the balance between heat transfer efficiency and pressure drop in the gas stream. Accordingly, a continuing need exists for a heat exchange apparatus for gas streams combining a corrosion resistant material with a configuration that provides good heat transfer efficiency with minimum pressure drop.